Process for preparing certain pyridine 2,3,6-triones

ABSTRACT

New silver dye-bleach catalysts and the process for their manufacture are provided. These compounds have the general formula ##STR1## wherein A is an electron-withdrawing group and R 1  and R 2  are hydrogen, optionally substituted alkyl or optionally substituted aryl.

This is a division of application Ser. No. 123,867, filed Feb. 22, 1980 now U.S. Pat. No. 4,288,598, issued Sept. 8, 1981.

This invention relates to novel pyridine-triones compounds, to their production and to their use as silver dye-bleach catalysts in photographic processes.

According to the present invention these are provided compounds of the general formula ##STR2## wherein A is an electron-withdrawing group, and R₁ and R₂ are hydrogen, optionally substituted alkyl or optionally substituted aryl.

Examples of suitable groups A are cyano and carboxamide. Alkyls for R₁ and R₂ contain 1 to 6, preferably 1 to 4 carbon atoms. Aryl represents mono- or bicyclic, saturated or aromatic ring systems, preferably phenyl. Substituents of these alkyl groups are alkoxy with 1 to 4 carbon atoms, hydroxy or halogen, such as fluorine, chlorine or bromine. The aryl (phenyl) groups may be substituted by the same substituents and further by alkyl of 1 to 4 carbon atoms.

Examples of compounds of formula (1) are compounds of formulae ##STR3## wherein R₃ and R₄ are each alkyl of 1 to 4 carbon atoms.

A particularly useful compound of formula (2) is the compound of formula ##STR4## and the compound of formula ##STR5##

A particularly useful compound of formula (3) is the compound of formula ##STR6##

Compounds of formula (1) may be prepared by hydrolysis using aqueous acid of an azomethine compound of formula ##STR7## wherein A, R₁ and R₂ have the meanings assigned to them above and R₅ comprises an optionally substituted aryl or an optionally substituted heterocyclic ring.

Preferably, R₅ N comprises an optionally substituted p-phenylene diamine residue.

Alternatively, compounds of formula (1) may be prepared from hydroxy-pyridones of formula ##STR8## wherein A, R₁ and R₂ have the meanings assigned to them above, by reaction with a nitroso compound R₅ NO, wherein R₅ has the meaning assigned to it above. Compounds of formula (7) are possible intermediates in this reaction.

The compounds of formula (1) are useful as silver dye-bleach catalysts in photographic processes. They are especially useful in a photographic process which involves contacting a preformed silver photographic image with a coating of a reducible dye such as an azomethine or triphenyl-methane dye, and processing with a solution of the compound of formula (1) together with an acid and a silver complexing agent, causing the compound of formula (1) to be reduced imagewise to an active dihydro form, which diffuses imagewise into the dye layer and bleaches it imagewise, leaving a dye image which is the negative of the original silver image.

Suitable dyes for the above process are azomethine or triphenylmethane dyes, including particularly those of formula (7) when R₅ N comprises a substituted paraphenylene diamine residue. Suitable silver complexing agents are chloride, bromide or iodide ions or thiourea.

EXAMPLE 1 5-Cyano-1-ethyl-4-methylpyridine-2,3,6-trione

1.02 g of 3-Cyano-1-ethyl-4-methyl-5-[4-(N-ethyl-N-hydroxyethylamino)phenylimino]-pyridine-2,6-dione (prepared as described in German Offenlegungsschrift No. 2808825) is stirred in 7 ml of water, and concentrated hydrochloric acid is slowly added until the blue dye had disappeared. A pale yellow solid precipitates, and is filtered off and recrystallised from ethyl acetate/petrol, yield 0.32 g, m.p. 159°-160° C. This is the compound of formula (4).

EXAMPLE 2 1,4-Dimethylpyridine-5-carboxamide-2,3,6-trione

0.91 g of 1,4-Dimethyl-6-hydroxypyrid-2-one-3-carboxamide and 0.75 g of N,N-dimethyl-4-nitrosoaniline are stirred in 20 ml of acetic acid for 1 hour, and then 10 ml of water and 10 ml of concentrated hydrochloric acid are added. A yellow solid slowly precipitates and is filtered off. Yield 0.43 g, m.p. 210°-215° C. (dec.). This is the compound of formula (6).

EXAMPLE 3 1-Butyl-5-cyano-4-methylpyridine-2,3,6-trione

Prepared using the method of Example 2, with 1.03 g of 1-butyl-3-cyano-6-hydroxy-4-methylpyrid-2-one and 0.76 g of dimethyl-nitrosoaniline. Recrystallised from petrol/ethyl acetate, yield 0.54 g, m.p. 134°-135° C. This is the compound of formula (5).

EXAMPLE 4 Bleaching of an azomethine dye

An assembly is prepared which comprises a transparent cellulose triacetate film base 150 microns thick having coated thereon a layer which comprises 10 mg/dm² of compound of formula ##STR9## in 30 mg/dm² of gelatin.

A strip of this coated assembly and a strip of a silver image print of a bar chart ranging in frequency from 0.11 to 10 line pairs per mm are contacted face to face with a processing solution of the following composition:

    ______________________________________                                         Compound of formula (4) 10     mg                                              2-ethoxy ethanol        0.5    ml                                              added to hydrochloric acid (0.25N)                                                                     100    ml.                                             ______________________________________                                    

After a contact time of 1 minute, an image of the bar chart is produced in the dye coating, giving an 88% response at 10 lines/mm.

EXAMPLE 5 Bleaching of a triphenylmethane dye.

Similar strips are taken as in Example 4, but the dye rosaniline of formula ##STR10## is used.

After 1 minute contact time a magenta image was seen in the dye layer. 

I claim:
 1. A process for the preparation of a compound of the formula ##STR11## which comprises hydrolysing, using aqueous acid, an azomethine compound of the formula ##STR12## wherein R₅ is a N,N-dimethylaniline residue, A is cyano or carboxamide, and R₁ and R₂ are hydrogen, alkyl of 1 to 6 carbon atoms, alkyl substituted by hydroxy, halogen or alkoxy of 1 to 4 carbon atoms, phenyl or phenyl substituted by hydroxy, halogen, alkyl or alkoxy of each 1 to 4 carbon atoms.
 2. A process for the preparation of a compound according to claim 1 which comprises reacting a hydroxypyridone of formula ##STR13## with a nitroso compound R₅ NO, wherein A, R₁, R₂ and R₅ have the meanings assigned to them in claim
 1. 3. A process for the preparation of a compound according to claim 1 of the formula ##STR14## wherein R₃ and R₄ are each alkyl of 1 to 4 carbon atoms.
 4. A process for the preparation of a compound according to claim 3 of the formula ##STR15##
 5. A process for the preparation of a compound according to claim 3 of the formula ##STR16##
 6. A process for the preparation of a compound according to claim 3 of the formula ##STR17## 